1. Field of Invention
The present invention relates to an air duct orifice, and more particularly, to an air duct orifice for reducing low frequency noise, having a structure by which discharge noise of an engine is transmitted to an engine room and introduction of foreign substances is prevented.
2. Description of the Related Art
Reducing noise in air ducts (also called intake pipes), has become an important focus of study in recent years. An example of an air duct for reducing engine noise is described in Korean utility model publication No. 1997-041460, which discloses a structure in which a protrusion portion having a discharging hole is formed on one side of an intake pipe. This structure is disadvantageous in that foreign substances can enter easily into the structure, and the engine noise reduction effect is insignificant.
As another example, Japanese unexamined utility model publication No. S55-180964 discloses a structure in which a cap for cleaning air is attached to an end of a pipe and an opening is formed on the cap for guiding air flow to the exterior. This structure is advantageous in that noise is discharged and an inflow of water is prevented, however the engine noise blocking effect is insignificant.
As yet another example, a large-capacity resonator has been used to reduce lower frequency engine booming. In the layout aspect, it is unfavorable to install a large resonator of 2.5 liters or more in a narrow space of the engine room and manufacturing costs and weight are increased.